Liquid fertilizer is commonly applied to an agricultural field before, during or after planting of a crop. A typical liquid fertilizer application system includes a tank for holding the liquid fertilizer, a pump for pumping the fertilizer from the tank, a plurality of distribution lines that eventually deliver the liquid to a delivery tube or spray nozzle, for placing the liquid on or in the soil near the plants. Down stream from the pump, various orifices, valves, etc are used to meter the volume of liquid directed to each crop row or outlet to deliver the desired application rate. The size of the pump is dependent on the width of the machine, i.e. the number of crop rows to be treated. Furthermore, the flow control orifices, and or valves must be customized for each row, taking into consideration the length of the line from the pump to the row. This adds considerable complexity to the manufacture of multiple machine models, types and widths.
As the cost of fertilizers and other inputs to an agricultural fields increase, it becomes more important to precisely control the application of inputs to the field to avoid excess application rates, overlaps in application, application to non-crop areas, etc. One such system for doing so is described in U.S. Pat. No. 7,395,769. This patent describes a liquid application system with a single pump supplying liquid to a number of bypass valves, one for each row. The bypass valves are controlled to vary the rate of liquid application at each row. This system requires a liquid return line for the bypassed liquid. Furthermore, the size of the pump must vary over a full line of implements widths, or a single maximum sized pump is used on all implements, adding unnecessary cost to those implements not needing the full capacity of the pump.